There have been many proposed structures for drills designed to drill concrete with metal reinforcement members embedded therein. The need for efficient drilling bits has been greatly increased by the construction techniques used in nuclear reactors and the like in which a very heavily reinforced concrete is used. Reinforcement bars are used to such an extent that prior art drills sometimes have to be changed many times before a hole can be completed therethrough.
The prior art shows a number of drills of the general type to which the present disclosure is related.
Typical drills having cutting faces using hardened cutting inserts are shown in U.S. Pat. Nos. 2,524,570 to Phipps; 2,856,157 to Chapin et al.; and 2,969,122 to Steffes. The latter patent shows hardened inserts raked away from the direction of travel of the bit, and this is also true of U.S. Pat. No. 2,856,157 set forth above.
U.S. Pat. No. 2,081,302 to Jarvis shows a combination bit having both hardened inserts and also chips set in its face, although all of these inserts appear to be on the same plane.
U.S. Pat. No. 2,511,991 to Nussbaum shows the combination of diamonds and carbide tips in the face of a cutting bit, and U.S. Pat. No. 3,066,749 to Hildebrandt is of a roughly similar type.